Fluorescence analysis of natural aquatic environments, such as including oceanic, estuarine, or fresh waters, can be based on measurements of water emission, such as in response to a laser, LED, Xenon flash tube, or other excitation sources. Fluorescence analysis can be used to retrieve information about the fluorescent constituents in a water body or sample. For example, in vivo fluorescence of chlorophyll-a (Chl-a) and accessory phycobiliprotein (PBP) pigments can be broadly used as an index of phytoplankton biomass, and can provide useful information for structural or photo-physiological characterization of mixed algal populations. A broadband chromophoric dissolved organic matter (CDOM) fluorescence emission can be used to assess CDOM abundance, or to assess qualitative characteristics of CDOM.
There can be significant spectral complexity of the actively stimulated emission of natural waters. This can be due to an overlap between water Raman (WR) scattering and the fluorescence bands of aquatic constituents. Most commercially available field fluorometers use spectrally broad excitation sources and relatively narrow discrete band emission detection, and often do not provide adequate spectral resolution to ensure reliable assessment of constituents in spectrally complex natural waters.
Spectral and temporal measurements of water emission can be performed using a various optical configurations. Some examples use a plurality of excitation sources that produce different excitation signals with different wavelengths. Hull et al., in U.S. Pat. No. 7,209,223, entitled OPTICAL DEVICE FOR MEASURING OPTICAL PROPERTIES OF A SAMPLE AND METHOD RELATING THERETO, refers to a device with a plurality of excitation sources positioned on a housing incident to a sample in a flow-through measurement cell, and detecting a continuous, broadband spectrum of emission wavelengths. Gilby, in U.S. Pat. No. 7,251,026, entitled FLUORESCENCE DETECTOR GEOMETRY, describes a photometric flow cell that uses a retro-reflecting mirror to increase a path-length of an excitation signal. Fluorescence and absorbance characteristics, such as over multiple wavelengths, can be detected. Schrieber et al., in U.S. Pat. No. 4,084,905, entitled APPARATUS FOR DETECTING AND MEASURING FLUORESCENCE EMISSION, refers to detecting and measuring a time course of fluorescence using a “Kautsky” apparatus that includes an excitation source, a filter, and photo-detector.